Frequency domain duplication in a long-range wireless local area network

ABSTRACT

A method for generating OFDM signals is implemented in a device operating according to a communication protocol. The protocol defines non-duplicate mode data units corresponding to single component channels of a BSS channel, and non-duplicate mode data units corresponding to sets of adjacent component channels. Non-duplicate mode data units corresponding to a set of component channels have more lower-edge and/or upper-edge guard tones than non-duplicate mode data units corresponding to single component channels. The method includes determining that a duplicate mode will be utilized for an OFDM transmission in the set of component channels and, in response, generating a duplicate mode data unit. The duplicate mode data unit has fewer lower-edge and/or upper-edge guard tones than a non-duplicate mode data unit corresponding to a set of component channels, and includes one duplicate of the non-duplicate mode data unit corresponding to the single component channel for each adjacent component channel.

CROSS-REFERENCES TO RELATED APPLICATIONS

This claims the benefit of U.S. Provisional Patent Application No.61/651,084, entitled “Frequency Domain 2 MHz (64FFT) Duplication in802.11ah” and filed on May 24, 2012, the disclosure of which isincorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to long range wireless local area networks.

BACKGROUND

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in thegigabits per second (Gbps) range.

Work has begun on two new standards, IEEE 802.11ah and IEEE 802.11af,each of which will specify wireless network operation in sub-1 GHzfrequencies. Low frequency communication channels are generallycharacterized by better propagation qualities and extended propagationranges compared to transmission at higher frequencies. In the past,sub-1 GHz ranges have not been utilized for wireless communicationnetworks because such frequencies were reserved for other applications(e.g., licensed TV frequency bands, radio frequency band, etc.). Thereare few frequency bands in the sub-1 GHz range that remain unlicensed,with different specific unlicensed frequencies in different geographicalregions. The IEEE 802.11ah Standard will specify wireless operation inavailable unlicensed sub-1 GHz frequency bands. The IEEE 802.11afStandard will specify wireless operation in TV White Space (TVWS), i.e.,unused TV channels in sub-1 GHz frequency bands.

SUMMARY

A method for generating orthogonal frequency division multiplexing(OFDM) signals to be transmitted in a basic service set (BSS) channel isimplemented in a communication device operating according to acommunication protocol. A set of two or more component channels iscollectively coextensive with the BSS channel. The communicationprotocol defines (i) a non-duplicate mode data unit corresponding to asingle component channel within the set of two or more componentchannels and (ii) a non-duplicate mode data unit corresponding to afirst set of adjacent component channels within the set of two or morecomponent channels. The non-duplicate mode data unit corresponding tothe single component channel has (i) a first number of lower-edge guardtones and (ii) a first number of upper-edge guard tones. Thenon-duplicate mode data unit corresponding to the first set of adjacentcomponent channels has (i) a second number of lower-edge guard tones and(ii) a second number of upper-edge guard tones. At least one of (i) thesecond number of lower-edge guard tones is greater than the first numberof lower-edge guard tones or (ii) the second number of upper-edge guardtones is greater than the first number of upper-edge guard tones. Themethod includes determining, at the communication device, that aduplicate mode will be utilized for a first OFDM transmission in thefirst set of adjacent component channels, and in response to determiningthat the duplicate mode will be utilized for the first OFDMtransmission, generating, at the communication device, a first duplicatemode data unit corresponding to the first set of adjacent componentchannels, such that the first duplicate mode data unit has one or bothof (i) less than the second number of lower-edge guard tones and (ii)less than the second number of upper-edge guard tones. The firstduplicate mode data unit includes, for each component channel in thefirst set of adjacent component channels, one duplicate, in frequency,of the non-duplicate mode data unit corresponding to the singlecomponent channel.

In another embodiment, a communication device includes a networkinterface configured to operate according to a communication protocol.The communication protocol defines (i) a non-duplicate mode data unitcorresponding to a single component channel within a set of two or morecomponent channels collectively coextensive with a basic service set(BSS) channel, and (ii) a non-duplicate mode data unit corresponding toa set of adjacent component channels within the set of two or morecomponent channels. The non-duplicate mode data unit corresponding tothe single component channel has (i) a first number of lower-edge guardtones and (ii) a first number of upper-edge guard tones. Thenon-duplicate mode data unit corresponding to the set of adjacentcomponent channels has (i) a second number of lower-edge guard tones and(ii) a second number of upper-edge guard tones, and at least one of (i)the second number of lower-edge guard tones is greater than the firstnumber of lower-edge guard tones or (ii) the second number of upper-edgeguard tones is greater than the first number of upper-edge guard tones.The network interface is also configured to determine that a duplicatemode will be utilized for an orthogonal frequency division multiplexing(OFDM) transmission in the set of adjacent component channels, and, inresponse to determining that the duplicate mode will be utilized for theOFDM transmission, generate a duplicate mode data unit corresponding tothe set of adjacent component channels, such that the duplicate modedata unit has one or both of (i) less than the second number oflower-edge guard tones and (ii) less than the second number ofupper-edge guard tones. The duplicate mode data unit includes, for eachcomponent channel in the set of adjacent component channels, oneduplicate, in frequency, of the non-duplicate mode data unitcorresponding to the single component channel.

In another embodiment, a nontransitory computer-readable medium storesinstructions for operating according to a communication protocol. Thecommunication protocol defines (i) a non-duplicate mode data unitcorresponding to a single component channel within a set of two or morecomponent channels collectively coextensive with a basic service set(BSS) channel and (ii) a non-duplicate mode data unit corresponding to aset of adjacent component channels within the set of two or morecomponent channels. The non-duplicate mode data unit corresponding tothe single component channel has (i) a first number of lower-edge guardtones and (ii) a first number of upper-edge guard tones. Thenon-duplicate mode data unit corresponding to the set of adjacentcomponent channels has (i) a second number of lower-edge guard tones and(ii) a second number of upper-edge guard tones. At least one of (i) thesecond number of lower-edge guard tones is greater than the first numberof lower-edge guard tones or (ii) the second number of upper-edge guardtones is greater than the first number of upper-edge guard tones. Theinstructions, when executed by one or more processors, cause the one ormore processors to determine that a duplicate mode will be utilized foran orthogonal frequency division multiplexing (OFDM) transmission in theset of adjacent component channels. The instructions also cause the oneor more processors to, in response to determining that the duplicatemode will be utilized for the OFDM transmission, generate a duplicatemode data unit corresponding to the set of adjacent component channels,such that the duplicate mode data unit has one or both of (i) less thanthe second number of lower-edge guard tones and (ii) less than thesecond number of upper-edge guard tones. The duplicate mode data unitincludes, for each component channel in the set of adjacent componentchannels, one duplicate, in frequency, of the non-duplicate mode dataunit corresponding to the single component channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN) in which a long range communication protocol is implemented,according to an embodiment.

FIG. 2 is an example channelization scheme for a long rangecommunication protocol, according to an embodiment.

FIGS. 3A, 3B, 3C and 3D are tone map diagrams, according to IEEE 802.11nand/or IEEE 802.11ac, of a 20 MHz legacy packet, a 20 MHz non-legacypacket, a true 40 MHz packet, and a legacy duplicate mode 40 MHz packet,respectively.

FIGS. 4A, 4B and 4C are example tone map diagrams of a 2 MHz long rangedata unit, a true 4 MHz long range data unit, and a duplicate mode 4 MHzlong range data unit, respectively, according to an embodiment.

FIGS. 5A and 5B are example tone map diagrams of a true 8 MHz long rangedata unit and a duplicate mode 8 MHz long range data unit, respectively,according to an embodiment.

FIGS. 6A and 6B are diagrams of an example long range data unit having ashort preamble format and an example long range data unit having a longpreamble format, respectively, according to an embodiment.

FIGS. 7A and 7B are diagrams of an example duplicate mode 4 MHz longrange data unit having the short preamble format of FIG. 6A, and anexample duplicate mode 4 MHz long range data unit having the longpreamble format of FIG. 6B, respectively, according to an embodiment.

FIG. 8 is a diagram of an example duplicate mode 4 MHz long range nulldata packet, according to an embodiment.

FIG. 9 is a flow diagram of an example method for generating orthogonalfrequency division multiplexing (OFDM) signals to be transmitted in abasic service set (BSS) channel, according to an embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmits datastreams to one or more client stations. The AP is configured to operatewith client stations according to at least one communication protocol.The communication protocol defines operation in a sub-1 GHz frequencyrange, and is typically used for applications requiring long rangewireless communication with relatively low data rates. The communicationprotocol (e.g., IEEE 802.11ah or IEEE 802.11af) is referred to herein asa “long range” communication protocol. In some embodiments, physicallayer (PHY) data units conforming to the long range communicationprotocol (“long range data units”) are the same as or similar to “shortrange” data units conforming to a higher frequency, shorter rangecommunication protocol (e.g., IEEE 802.11n, and/or IEEE 802.11ac), butare generated using a lower clock rate (e.g., by downclocking an IEEE802.11n or 802.11ac signal). In one embodiment, for example, the longrange communication protocol defines 2 MHz, 4 MHz, 8 MHz and 16 MHz dataunits that are substantially similar to IEEE 802.11n or 802.11ac 20 MHz,40 MHz, 80 MHz and 160 MHz data units, respectively, and are generatedusing the same inverse fast Fourier transform (IFFT) size as therespective IEEE 802.11n or 802.11ac data unit, but are generated using aten times slower clock rate than the respective IEEE 802.11n or 802.11acdata unit. Like IEEE 802.11n and IEEE 802.11ac short range data units,long range data units are transmitted on multiple subcarriers/tones,using orthogonal frequency division multiplexing (OFDM), over a wirelesschannel. Example formats of long range data units, according to variousembodiments, are described in U.S. patent application Ser. No.13/359,336, “Physical Layer Frame Format For Long Range WLAN,” thedisclosure of which is hereby incorporated by reference herein.

The IEEE 802.11n and 802.11ac Standards each define one or more“duplicate” modes in which some or all of a 20 MHz data unit (packet) isreplicated in two or more sub-bands of a 40 MHz or greater data unit.Frequency duplication allows combining at the receiver (e.g.,maximal-ratio combining), which can in turn increase receiversensitivity and provide extended range. Duplication can also provideimproved bandwidth protection within a basic service set (BSS), orbetween a BSS and a BSS of another AP (OBSS). Both IEEE 802.11n and802.11ac define a “legacy duplicate mode” in which the preamble and dataportion of a 20 MHz legacy packet (i.e., a data unit that can be decodedby an IEEE 802.11a or 802.11g compliant receiver) is replicated in each20 MHz sub-band of a 40 MHz or greater packet, with a different phaseshift factor being applied to each 20 MHz sub-band in order to reducethe peak-to-average power ratio (PAPR) of the OFDM signal. In addition,the IEEE 802.11n Standard defines a special modulation and coding scheme(MCS), “MCS32,” in which a 40 MHz signal duplicates a 6 megabits persecond (Mbps) data portion of a 20 MHz legacy packet in the lower andupper 20 MHz sub-bands, while the 40 MHz signal preamble includes ashort training field (STF), long training field (LTF), and signal (SIG)field that instead follows the preamble of a true 40 MHz packet. As usedherein, the modifier “true” is used to indicate that a data unit (e.g.,packet) does not utilize frequency duplication (e.g., does not duplicatea preamble, preamble portion, and/or data portion of a narrowerbandwidth data unit within each of multiple sub-bands). As in the legacyduplicate mode of IEEE 802.11n and 802.11ac, the MCS32 duplicate modeapplies a different phase shift factor to each 20 MHz sub-band in orderto reduce the PAPR of the OFDM signal. The MCS32 duplicate mode of IEEE802.11n, and the legacy duplicate mode of IEEE 802.11n and 802.11ac, arediscussed in more detail below with reference to FIGS. 3A-3D. As will beseen, 20 MHz legacy packets each include a larger number of upper-edgeand lower-edge guard tones (in the LTF and the data portion) as comparedto a 20 MHz non-legacy packet, which provides certain advantages whenusing the IEEE 802.11n/ac legacy duplicate mode or IEEE 802.11n MCS32duplicate mode. In some embodiments where the long range communicationprotocol defines long range data units that are substantially similar todown-clocked versions of IEEE 802.11n or 802.11ac signals, the longrange communication protocol, however, does not define any down-clockedversions of legacy packets. Thus, in these embodiments, the long rangecommunication protocol does not define a legacy duplicate mode, and doesnot support a down-clocked version of the MCS32 duplicate mode in whicha legacy data portion is duplicated in each of multiple sub-bands. As aresult, a different approach is required if the long range communicationprotocol is to provide a duplicate mode for increased receiversensitivity. Various embodiments of such an approach are describedbelow, along with a more detailed description of the duplicate modescurrently defined under the IEEE 802.11n and 802.11ac Standards.

FIG. 1 is a block diagram of an example WLAN 10 in which a long rangecommunication protocol is implemented, according to an embodiment. TheWLAN 10 includes an AP 14 having a host processor 15 coupled to anetwork interface 16. The network interface 16 includes a medium accesscontrol (MAC) processing unit 18 and a physical layer (PHY) processingunit 20. The PHY processing unit 20 includes a plurality of transceivers21, and the transceivers 21 are coupled to a plurality of antennas 24.Although three transceivers 21 and three antennas 24 are illustrated inFIG. 1, the AP 14 can include different numbers (e.g., 1, 2, 4, 5, etc.)of transceivers 21 and antennas 24 in other embodiments.

The WLAN 10 further includes a plurality of client stations 25. Althoughfour client stations 25 are illustrated in FIG. 1, the WLAN 10 caninclude different numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations25 in various scenarios and embodiments. The client station 25-1includes a host processor 26 coupled to a network interface 27. Thenetwork interface 27 includes a MAC processing unit 28 and a PHYprocessing unit 29. The PHY processing unit 29 includes a plurality oftransceivers 30, and the transceivers 30 are coupled to a plurality ofantennas 34. Although three transceivers 30 and three antennas 34 areillustrated in FIG. 1, the client station 25-1 can include differentnumbers (e.g., 1, 2, 4, 5, etc.) of transceivers 30 and antennas 34 inother embodiments.

In some embodiments, one, some, or all of the client stations 25-2,25-3, and 25-4 has/have a structure the same as or similar to the clientstation 25-1. In these embodiments, the client stations 25 structuredthe same as or similar to the client station 25-1 have the same or adifferent number of transceivers and antennas. For example, the clientstation 25-2 has only two transceivers and two antennas (not shown),according to an embodiment.

In an embodiment, the PHY processing unit 20 of the AP 14 is configuredto generate data units conforming to the long range communicationprotocol, and the transceiver(s) 21 is/are configured to transmit thegenerated data units via the antenna(s) 24. Similarly, the PHYprocessing unit 20 of the AP 14 is configured to process received dataunits conforming to the long range communication protocol, in anembodiment, with the data units being received by the transceiver(s) 24via the antenna(s) 24. Data units conforming to the long range protocolwill be described with reference to FIGS. 4-8 below, according tovarious different embodiments.

In an embodiment, the PHY processing unit 29 of the client device 25-1is also configured to generate data units conforming to the long rangecommunication protocol, and the transceiver(s) 30 is/are configured totransmit the generated data units via the antenna(s) 34. Similarly, thePHY processing unit 29 of the client device 25-1 is configured toprocess received data units conforming to the long range communicationprotocol, in an embodiment, with the data units being received by thetransceiver(s) 30 via the antenna(s) 34.

FIG. 2 is a diagram of an example channelization scheme 40 for a longrange communication protocol, according to an embodiment. Thechannelization scheme 40 is utilized for data stream transmissions in aWLAN (e.g., the WLAN 10 of FIG. 1), in an embodiment. For example, oneor more channels within the channelization scheme 40 are used for OFDMtransmissions from AP 14 to client station 25-1 of FIG. 1, and/or viceversa, in various embodiments and/or scenarios. Within thechannelization scheme 40, in various different scenarios, “component”channels 42 are utilized individually for data transmissions, or areconcatenated to form a larger communication channel, in an embodiment.In some embodiments, there may be more or fewer component channels 42than illustrated in FIG. 2.

In some embodiments, two adjacent component channels 42 can beconcatenated to form a channel 44. For example, component channels 42-1and 42-2 can be concatenated to form channel 44-1. Similarly, componentchannels 42-3 and 42-4 can be concatenated to form channel 44-2.Moreover, in some embodiments, four adjacent component channels 42 canbe concatenated to form a channel 46. For example, component channels42-1 through 42-4 can be concatenated to form channel 46-1. Similarly,component channels 42-5 through 42-8 can be concatenated to form channel46-2. Further, in some embodiments, eight adjacent component channels 42can be concatenated to form a channel 48. For example, componentchannels 42-1 through 42-8 can be concatenated to form channel 48-1.

In an embodiment, an AP (e.g., AP 14 of FIG. 1) assigns a priority toone or more of the component channels 42 when establishing a BSS. In oneembodiment, for example, the AP designates one of the channels 42 as a“primary” channel, and one or more of the component channels 42 as a“secondary” channel. In some embodiments, one or more additionalpriority levels (“tertiary,” etc.) are also assigned to other componentchannels 42. The assigned primary, secondary, etc., component channels42 are monitored for media access control purposes (i.e., to determinean available channel for data transmissions within the BSS), in anembodiment.

In the example channelization scheme 40, each component channel 42 has abandwidth of 2 MHz, each channel 44 has a bandwidth of 4 MHz, eachchannel 46 has a bandwidth of 8 MHz, and the channel 48-1 has abandwidth of 16 MHz. In other embodiments, each component channel 42 hasa different, suitable bandwidth, such as 1 MHz, 5 MHz, 10 MHz, 20 MHz,etc. In one embodiment, long range data units are generated by the AP(e.g., AP 14) or the client station (e.g., client station 25-1) to havea bandwidth equal to the bandwidth of the widest available channel ofthe channels 42, 44, 46 and 48. In one embodiment, the widest availablechannel is the channel that satisfies one or more media access rules. Inone embodiment, for example, any BSS channel must include the componentchannel 42 which the AP designated as the primary channel (i.e., notransmission is permitted unless the primary channel is determined to beidle). More generally, in some embodiments, a component channel 42 thathas a lower priority is treated as busy (regardless of whether thecomponent channel 42 is busy or idle) if another component channel 42having a higher priority is determined to be busy. Example media accesstechniques using primary, secondary, etc., channel designations,according to various embodiments, are described in U.S. patentapplication Ser. No. 13/034,409, “Methods and Apparatus for Determininga Composite Channel,” the disclosure of which is hereby incorporated byreference herein.

FIGS. 3A-3D are diagrams of tone map diagrams of data units (packets)conforming to the currently available IEEE 802.11n and/or 802.11acStandards. Referring first to FIG. 3A, the tone map 50 is an OFDM tonemap of the LTF and data portion of a 20 MHz legacy packet that can bedecoded by legacy IEEE 802.11a or 802.11g devices. The tone map 50includes low-side non-zero tones 52-1 and high-side non-zero tones 52-2.With specific reference to the data portion, the tone map 50 includes 24low-side data tones and two low-side pilot tones within tones 52-1, andincludes 24 high-side data tones and two high-side pilot tone withintones 52-2. The tone map 50 also includes a DC (null) tone 54, sixlower-edge guard (null) tones 56-1, and five upper-edge guard (null)tones 56-2.

The tone map 60 of FIG. 3B is an OFDM tone map of the LTF and dataportion of a non-legacy 20 MHz packet conforming to the IEEE 802.11n and802.11ac Standards. The tone map 60 includes low-side non-zero tones62-1 and high-side non-zero tones 62-2. With specific reference to thedata portion, the tone map 60 includes 26 low-side data tones and twolow-side pilot tones within tones 62-1, and includes 26 high-side datatones and two high-side pilot tone within tones 62-2. The tone map 60also includes a DC (null) tone 64, four lower-edge guard (null) tones66-1, and three upper-edge guard (null) tones 66-2. Thus, the 20 MHznon-legacy packet with tone map 60 has two fewer lower-edge guard tones,and two fewer upper-edge guard tones, than the 20 MHz legacy packet withtone map 50 of FIG. 3A.

The tone map 70 of FIG. 3C is an OFDM tone map of the LTF and dataportion of a true (non-duplicate mode) 40 MHz packet conforming to theIEEE 802.11n and 802.11ac Standards. The tone map 70 includes low-sidenon-zero tones 72-1 and non-zero high-side tones 72-2. With specificreference to the data portion, the tone map 70 includes 54 low-side datatones and three low-side pilot tones within tones 72-1, and includes 54high-side data tones and three high-side pilot tone within tones 72-2.The tone map 70 also includes three DC (null) tones 74, six lower-edgeguard (null) tones 76-1, and five upper-edge guard (null) tones 76-2.Thus, the true 40 MHz packet with tone map 70 has the same number oflower-edge and upper-edge guard tones as the 20 MHz legacy packet (tonemap 50), and both the true 40 MHz packet and the 20 MHz legacy packethave more lower-edge and upper-edge guard tones than the 20 MHznon-legacy packet (tone map 60).

In order to avoid a scenario in which duplicate mode 40 MHz (or wider)packets necessitate tighter filter design requirements than true 40 MHz(or wider) packets, the IEEE 802.11n and 802.11ac Standards do notdefine any mode or data unit in which 20 MHz non-legacy packets havingthe tone map 60 are duplicated in two or more sub-bands of a widerbandwidth signal. Instead, as stated above, the IEEE 802.11n and802.11ac Standards define a legacy duplicate mode in which a full(preamble and data portion) 20 MHz legacy packet is duplicated in two ormore sub-bands, and IEEE 802.11n further defines an MCS32 duplicate modein which the data portion of a legacy packet is duplicated in twosub-bands but the preamble portion is the same as a true 40 MHz packet.

The tone map 80 of FIG. 3D is an OFDM tone map of the LTF and dataportion of a legacy duplicate mode 40 MHz packet conforming to the IEEE802.11n and 802.11ac Standards. The tone map 80 includes low-sidenon-zero tones 82-1 and high-side non-zero tones 82-2. Because tone map80 corresponds to the legacy duplicate mode, tones 82-1 are identical totones 52-1, 54 and 52-2 of the 20 MHz legacy data unit shown in tone map50, and tones 82-2 are also identical to tones 52-1, 54 and 52-2 of the20 MHz legacy data unit shown in tone map 50. The tone map 80 alsoincludes 11 DC (null) tones 84, six lower-edge guard (null) tones 86-1,and five upper-edge guard (null) tones 86-2.

Because packets in the legacy duplicate mode utilize frequencyduplication of the 20 MHz legacy packet (tone map 50) for both the LTFand the data portion, six lower-edge guard tones and five upper-edgeguard tones are maintained throughout the legacy duplicate mode packet.Thus, the legacy duplicate mode 40 MHz packet has the same guard toneprotection as the true 40 MHz packet corresponding to tone map 70 ofFIG. 3C. Accordingly, for a packet with a given bandwidth, the sametransmit/receive filter design requirements can be used regardless ofwhether the packet corresponds to the legacy duplicate mode. Transmitand receive filtering requirements are typically dictated by the bandedge that corresponds to the smaller number of guard tones. For example,the transmit/receive filter design requirements for a packet with sixlower-edge guard tones and five upper-edge guard tones would typicallybe dictated by the five upper-edge guard tones.

In the MCS32 duplicate mode of the IEEE 802.11n Standard, a 40 MHz dataunit utilizes the preamble of a true 40 MHz data unit, while the dataportion is the same as in the legacy duplicate mode (i.e., the dataportion consists of a frequency duplicate of a 20 MHz legacy packetwithin each of the two 20 MHz sub-bands). Accordingly, an MCS32duplicate mode 40 MHz packet has an LTF with the tone map 70, and a dataportion with the tone map 80. Thus, as in the legacy duplicate mode, theMCS32 duplicate mode 40 MHz packet provides the same number oflower-edge and upper-edge guard tones as a true 40 MHz packet, andallows the same transmit/receive filter design requirements as the true40 MHz packet. By using a true 40 MHz packet preamble, however, theMCS32 duplicate mode does not allow a receiver to utilize combiningtechniques when decoding the SIG field, which can create a bottleneckfor receiver sensitivity.

Notably, the non-zero tones of the LTF of a 20 MHz legacy packet havethe same tone values as the respective non-zero tones in each of theupper and lower 20 MHz sub-bands of a true 40 MHz packet LTF. Thus, theMCS32 duplicate mode 40 MHz packet, like the legacy duplicate mode 40MHz packet, has the property that each 20 MHz sub-band can appear to areceiving device as a stand-alone 20 MHz legacy data unit.

In some embodiments, a long range communication protocol utilizesfrequency duplication to provide BSS and/or OBSS bandwidth protection,and/or to increase receiver sensitivity, but does not define any dataunits that correspond to down-clocked versions of legacy packets (orportions thereof). Thus, in these embodiments, the long rangecommunication protocol cannot utilize down-clocked versions of eitherthe MCS32 duplicate mode data unit (duplicating the data portion of alegacy packet) or the legacy duplicate mode data unit (duplicating theentire legacy packet). Accordingly, in these embodiments, the long rangecommunication protocol must use a technique different than that of theIEEE 802.11n and 802.11ac Standards in order to generate duplicate modedata units. In one embodiment, a duplicate mode, long range data unit(e.g., packet) is generated by duplicating a non-legacy,narrower-bandwidth long range data unit in each of two or moresub-bands. In one embodiment, for example, a non-legacy, long range dataunit corresponding to a narrowest possible BSS channel bandwidth isduplicated in each sub-band. For ease of explanation, the long rangecommunication protocol is described below with reference to anembodiment that utilizes a channelization scheme similar to that shownin FIG. 2, such that the narrowest possible BSS channel bandwidth is 2MHz, and such that a duplicate mode or non-duplicate mode long rangedata unit has a bandwidth of 2 MHz, 4 MHz, 8 MHz or 16 MHz, depending onthe BSS channel.

FIGS. 4A, 4B and 4C are example tone map diagrams of a 2 MHz long rangedata unit, a true 4 MHz long range data unit (formed without usingfrequency duplication), and a duplicate mode 4 MHz long range data unit,respectively, according to one embodiment. The tone maps of FIGS. 4A-4Crepresent tones for at least the data portion of the respective dataunit. In various embodiments and/or scenarios, the tone maps of FIGS.4A-4C correspond to long range data units generated by the PHYprocessing unit 20 of AP 14 or the PHY processing unit 29 of clientstation 25-1 in FIG. 1.

Referring first to FIG. 4A, a tone map 200 shows that a 2 MHz long rangedata unit includes low-side non-zero tones 202-1 and high-side non-zerotones 202-2. In one embodiment, for example, and with reference to adata portion of the 2 MHz long range data unit, the tone map 200includes 26 low-side data tones and two low-side pilot tones withintones 202-1, and includes 26 high-side data tones and two high-sidepilot tones within tones 202-2. The tone map 200 also includes a DC(null) tone 204, four lower-edge guard (null) tones 206-1, and threeupper-edge guard (null) tones 206-2. In an embodiment, the tone map 200is generated using a 64-point IFFT. Moreover, in an embodiment, the 2MHz long range data unit corresponding to tone map 200 is a 10×down-clocked version of a 20 MHz non-legacy packet as defined by theIEEE 802.11n or 802.11ac Standard.

Referring next to FIG. 4B, a tone map 220 shows that a true 4 MHz longrange data unit, formed without frequency duplication, includes low-sidenon-zero tones 222-1 and high-side non-zero tones 222-2. In oneembodiment, for example, and with reference to a data portion of thetrue 4 MHz long range data unit, the tone map 220 includes 54 low-sidedata tones and three low-side pilot tones within tones 222-1, andincludes 54 high-side data tones and three high-side pilot tones withintones 222-2. The tone map 220 also includes three DC (null) tones 224,six lower-edge guard (null) tones 206-1, and five upper-edge guard(null) tones 206-2. In various embodiments, the tone map 220 isgenerated using a 128-point IFFT, or two 64-point IFFTs in parallel,etc. Moreover, in an embodiment, the true 4 MHz long range data unitcorresponding to tone map 220 is a 10× down-clocked version of a true 40MHz data unit as defined by the IEEE 802.11n or 802.11ac Standard.

FIG. 4C shows a tone map 240 corresponding to a duplicate mode 4 MHzlong range data unit, where the data unit is generated by duplicatingthe 2 MHz long range data unit corresponding to tone map 200 in each 2MHz sub-band, e.g., to improve receiver sensitivity and/or provide morerobust channel protection as compared to the true 4 MHz long range dataunit. The tone map 240 includes low-side non-zero tones 242-1 andhigh-side non-zero tones 242-2. In one embodiment, for example, and withreference to a data portion of the duplicate mode 4 MHz long range dataunit, the tone map 240 includes 52 low-side data tones and four low-sidepilot tones within tones 242-1, and includes 52 high-side data tones andfour high-side pilot tones within tones 242-2. The tone map 240 alsoincludes seven DC (null) tones 244, four lower-edge guard (null) tones246-1, and three upper-edge guard (null) tones 246-2. In an embodiment,the tones at indices −64 to −1 of tone map 240 are identical to thetones at indices −32 to +31, respectively, of tone map 200, and thetones at indices 0 to +63 of tone map 240 are also identical to thetones at indices −32 to +31, respectively, of tone map 200.

In other embodiments, the tone maps 200, 220 and/or 240 includedifferent numbers of non-zero tones (e.g., data tones and/or pilottones), DC tones, lower-edge guard tones, and/or upper-edge guard tonesthan are shown in FIGS. 4A-4C. As in FIGS. 4A-4C, however, the tone map200 in each of these alternative embodiments includes fewer lower-edgeand upper-edge guard tones than tone map 220 of the true 4 MHz longrange data unit, which in turn causes the duplicate mode tone map 240 toinclude fewer lower-edge and upper-edge guard tones than tone map 220.In these alternative embodiments, as in the embodiment shown in FIGS.4A-4C, the reduced number of guard tones in the duplicate mode 4 MHzlong range data unit (tone map 240) gives rise to more stringenttransmit and/or receive filter requirements as compared to the true 4MHz long range data unit (tone map 220).

In an embodiment, the long range communication protocol also supportsone or more types of duplicate mode signals that have a bandwidthgreater than 4 MHz. FIGS. 5A and 5B correspond to one embodiment inwhich an 8 MHz long range data unit may be generated either as a true 8MHz long range data unit or a duplicate mode 8 MHz long range data unit.The tone maps of FIGS. 5A and 5B represent tones for at least the dataportion of the respective data unit. In various embodiments and/orscenarios, the tone maps of FIGS. 5A and 5B correspond to long rangedata units generated by the PHY processing unit 20 of AP 14 or the PHYprocessing unit 29 of client station 25-1 in FIG. 1.

Referring first to FIG. 5A, the tone map 300 shows that a true 8 MHzlong range data unit, without frequency duplication, includes low-sidenon-zero tones 302-1 and high-side non-zero tones 302-2. In oneembodiment, for example, and with reference to a data portion of thetrue 8 MHz long range data unit, the tone map 300 includes 117 low-sidedata tones and four low-side pilot tones within tones 302-1, andincludes 117 high-side data tones and four high-side pilot tones withintones 302-2. The tone map 300 also includes three DC (null) tones 304,six lower-edge guard (null) tones 306-1, and five upper-edge guard(null) tones 306-2. In various embodiments, the tone map 300 isgenerated using a 256-point IFFT, or four 64-point IFFTs in parallel,etc. Moreover, in an embodiment, the true 8 MHz long range data unitcorresponding to tone map 300 is a 10× down-clocked version of a true 80MHz data unit as defined by the IEEE 802.11ac Standard.

FIG. 5B shows a tone map 320 corresponding to another 8 MHz long rangedata unit, in which the data unit is generated by duplicating the 2 MHzlong range data unit (corresponding to tone map 200 of FIG. 4A) withineach 2 MHz sub-band, e.g., to improve receiver sensitivity and/orprovide more robust channel protection as compared to the true 8 MHzlong range data unit having tone map 300. The tone map 320 includeslow-side non-zero tones 322-1 and 322-2, and high-side non-zero tones322-3 and 322-4. The tone map 240 also includes seven DC (null) tones324, four lower-edge guard (null) tones 330-1, and three upper-edgeguard (null) tones 330-2. In an embodiment, the set of tones at indices−128 to −65 of tone map 320, the set of tones at indices −64 to −1 oftone map 320, the set of tones at indices 0 to +63 of tone map 320, andthe set of tones at +64 to +127 of tone map 320 are each identical tothe respective tones at indices −32 to +31 of tone map 200 in FIG. 4A.In various embodiments, the tone map 320 is generated using a 256-pointIFFT, or four 64-point IFFTs in parallel, etc.

Other embodiments of tone maps 300 and/or 320 include different numbersof non-zero tones (e.g., data tones and/or pilot tones), DC tones,lower-edge guard tones, and/or upper-edge guard tones than are shown inFIGS. 5A and 5B. As with the embodiment shown in FIGS. 5A and 5B,however, the tone map 320 in each of these alternative embodimentsincludes fewer lower-edge and upper-edge guard tones than tone map 300(for a true 8 MHz long range data unit), which in turn causes theduplicate mode tone map 320 to include fewer lower-edge and upper-edgeguard tones than tone map 300. In these alternative embodiments, as inthe embodiment of FIGS. 5A and 5B, the reduced number of guard tones inthe duplicate mode 8 MHz long range data unit (tone map 320) gives riseto more stringent transmit and/or receive filter requirements ascompared to the true 8 MHz long range data unit (tone map 300).

In some embodiments, the duplicate mode can also be used for still widerbandwidth signals. In one embodiment, for example, the long rangecommunication protocol supports the 4 MHz duplicate mode correspondingto tone map 240 of FIG. 4C, the 8 MHz duplicate mode corresponding totone map 320 of FIG. 5B, and a 16 MHz duplicate mode (not shown in thefigures). In one such embodiment, true 16 MHz long range data units aregenerated such that each 8 MHz sub-band is the same as the true 8 MHzlong range data unit (with tone map 300), and duplicate mode 16 MHz longrange data units are generated such that each 8 MHz sub-band is the sameas the duplicate mode 8 MHz long range data unit (with tone map 320). Inthis embodiment, the duplicate mode 16 MHz long range data unit givesrise to more stringent transmit and/or receive filter designrequirements than the true 16 MHz long range data unit, similar to the 4MHz and 8 MHz data units discussed above. In an embodiment, the true 16MHz long range data unit is a 10× down-clocked version of a true 160 MHzdata unit as defined by the IEEE 802.11ac Standard.

In some embodiments, each long range data unit can have one of multipledifferent preamble formats, such as the preamble formats shown in FIGS.6A and 6B. FIG. 6A is a diagram of an example long range data unit 400having a “short preamble” format, according to one such embodiment. Thelong range data unit 400 includes a short preamble 402 and a dataportion 404. In the example embodiment of FIGS. 6A and 6B, the shortpreamble 402 includes an STF 410 with two OFDM symbols, a first LTF(LTF1) 412 with two OFDM symbols, a SIG field 414 with two OFDM symbols,and a total of N−1 additional LTFs (416-1 through 416-N) each having oneOFDM symbol. In an embodiment, the STF 410 is used for packet detectionand automatic gain control, the LTFs 412 and 416-1 through 416-N areused for channel estimation, and the SIG field 414 indicates certain PHYcharacteristics of the data unit (e.g., length or duration, MCS, etc.).In an embodiment, the short preamble 402 includes one LTF for eachmultiple input multiple output (MIMO) spatial stream (e.g., for twospatial streams, such that the short preamble 402 includes LTF1 412 andLTF2 416-1, but no additional LTFs). In an embodiment, the long rangedata unit 400 has the same format as an IEEE 802.11n data unit with a“Greenfield” preamble format.

FIG. 6B is a diagram of an example long range data unit 420 having a“long preamble” format. The long range data unit 420 includes a longpreamble 422 and a data portion 424. In the example embodiment of FIGS.6A and 6B, the long preamble 422 includes a first, legacy STF (L-STF)430 with two OFDM symbols, a first, legacy LTF (L-LTF1) 432 with twoOFDM symbols, a first, legacy SIG (SIGA) field 434 with two OFDMsymbols, a second, non-legacy STF 440 with one OFDM symbol, N−1additional, non-legacy LTFs (442-1 through 442-N) each having one OFDMsymbol, and a second, non-legacy SIG (SIGB) field 444 with one OFDMsymbol. In an embodiment, the long preamble format of long range dataunit 420 is used when in a multi-user mode, and the LTFs 442 of the longpreamble 422 include one LTF per user. In some embodiments, a receivercan auto-detect whether a long range data unit has the short or longpreamble format by determining the modulation type of one or more OFDMsymbols within the first SIG field (i.e., SIG field 414 in long rangedata unit 400, or SIGA field 434 in long range data unit 420). In anembodiment, the long range data unit 420 has the same format as an IEEE802.11n data unit with a “mixed mode” preamble format, or the sameformat as an IEEE 802.11ac data unit.

In some embodiments, duplicate mode long range data units include notonly frequency duplicates of the data portion of a 2 MHz long range dataunit, but also frequency duplicates of the preamble portion of a 2 MHzlong range data unit. In one embodiment in which a 2 MHz long range dataunit has a preamble with an STF, LTF, and SIG field, for example, aduplicate mode, 4 MHz or greater long range data unit duplicates the 2MHz STF in each 2 MHz sub-band, duplicates the 2 MHz LTF in each 2 MHzsub-band (e.g., resulting in the tone map 240 of FIG. 4C for the LTFtones, in an embodiment), and duplicates the 2 MHz SIG field in each 2MHz sub-band. By duplicating a 2 MHz signal LTF rather than using a true4 MHz (or greater) long range data unit preamble, a receiving device canobtain valid channel estimation across all non-zero tones of the dataportion of the duplicate mode, long range data unit.

In other embodiments, however, duplicate mode long range data unitsinstead use the tone plan of a true 4/8/16 MHz long range data unit forthe LTF. For example, in one embodiment where duplicate mode 4 MHz longrange data units have a data portion with tone plan 240 of FIG. 4C, theLTF of the duplicate mode 4 MHz long range data unit instead has thetone plan 220 of FIG. 4B. In such an embodiment, receiver performancemay be degraded at the lower and upper 2 MHz sub-bands due to the factthat the data portion in each of those sub-bands has two more tones thanthe corresponding 2 MHz portion of the LTF in those sub-bands.

In one embodiment where duplicate mode long range data units duplicatethe preamble as well as the data portion, the fields within eachduplicated 2 MHz SIG field are the same as the fields within astand-alone 2 MHz long range data unit (e.g., include a bandwidth field,an MCS field, a coding field, etc., in an embodiment), and the bandwidthfield indicates a 2 MHz bandwidth. In this embodiment, each 2 MHzsub-band of the duplicate mode signal appears, to a receiving device, tobe the same as a stand-alone 2 MHz signal.

In one embodiment where long range data units can have either the shortpreamble format of FIG. 6A or the long preamble format of FIG. 6B, thelong range communication protocol supports the duplicate mode only forlong range data units that have the short preamble format. In anotherembodiment, the long range communication protocol supports the duplicatemode for long range data units having either a short or a long preambleformat. FIGS. 7A and 7B are diagrams of an example duplicate mode 4 MHzlong range data unit having the short preamble format of FIG. 6A, and anexample duplicate mode 4 MHz long range data unit having the longpreamble format of FIG. 6B, respectively, according to an embodiment.Referring first to FIG. 7A, the duplicate mode 4 MHz long range dataunit 500 includes a duplicated short preamble 502 and a duplicated dataportion 504. The duplicated short preamble 502 includes a duplicated STF510, LTF1 512, SIG field 514, and LTFs 516-1 through 516-N, with each 2MHz duplicate being the same (i.e., having the same tone map, and insome embodiments having the same SIG field contents) as STF 410, LTF1412, SIG field 414, and LTFs 416-1 through 416-N of FIG. 6A,respectively, in an embodiment. Each 2 MHz duplicate in the duplicateddata portion 504 is the same (i.e., has the same tone map) as the dataportion 404 of FIG. 6A, in an embodiment.

Referring next to FIG. 7B, the duplicate mode 4 MHz long range data unit520 includes a duplicated long preamble 522 and a duplicated dataportion 524. The duplicated long preamble 522 includes a duplicatedL-STF 530, L-LTF1 532, SIGA field 534, STF 536, LTFs 540-1 through540-N, and SIGB field 542, with each 2 MHz duplicate being the same(i.e., having the same tone map, and in some embodiments having the sameSIG field contents) as L-STF 430, L-LTF1 432, SIGA field 434, STF 440,LTFs 442-1 through 442-N, and SIGB field 444 of FIG. 6B, respectively,in an embodiment. Each 2 MHz duplicate in the duplicated data portion524 is the same (i.e., has the same tone map) as the data portion 424 ofFIG. 6B, in an embodiment.

In some embodiments, the long range communication protocol supports a“coordinated duplicate mode” in which the data plan and preamble areduplicated according to any of the embodiments described above, but inwhich the SIG field (e.g., duplicated SIG field 514 of FIG. 7A) or SIGAfield (e.g., duplicated SIGA field 534 of FIG. 7B) indicates a duplicatemode rather than indicating a 2 MHz signal. In one such embodiment, abandwidth field of the SIG/SIGA field indicates the full bandwidth ofthe duplicate mode long range data unit (e.g., 4 MHz, 8 MHz or 16 MHz,in an embodiment) to a receiving device, and an otherwiseunused/reserved MCS is used to indicate duplicate mode to the receivingdevice. In one embodiment where the long range communication protocoldefines an “MCS0” through “MCS9” for various non-duplicate modemodulation types and coding types/rates, but does not define an “MCS10,”for example, MCS10 is used to indicate the duplicate mode to a receiver.In one such embodiment, the long range communication protocol onlyallows a single modulation type and coding type/rate (e.g., BPSKmodulation at 1/2 BCC coding), and/or only a single number of spatialstreams (e.g., one spatial stream), for the duplicate mode.

In another embodiment in which a bandwidth field of the SIG/SIGA fieldindicates the full bandwidth of the duplicate mode long range data unit,an otherwise unused/reserved SIG/SIGA field bit combination, or a new“duplicate field” in the SIG/SIGA field, is used to indicate theduplicate mode to a receiver. In some of these embodiments, the longrange communication protocol allows any one of multiple differentmodulation types and/or coding types/rates for the duplicate mode. Anexample of this embodiment is shown in Table 1, for both a SIG field ina short preamble (e.g., the duplicated SIG field 514 in the shortpreamble format of long range data unit 500) and a SIG field in a longpreamble (e.g., the duplicated SIG field 534 in the long preamble formatof long range data unit 520):

TABLE 1 Short Preamble Long Preamble Length/Duration 9 9 MCS 4 —Bandwidth 2 2 Aggregation 1 — STBC 1 1 Coding 2 5 SGI 1 1 GID — 6 Nsts 28 PAID 9 — ACK Indication 2 2 Reserved 5 4 CRC 4 4 Tail 6 6 Total 48 48 In an embodiment, the various fields shown above are the same as thosedefined in the IEEE 802.11ac Standard, except for the “ACK indication”field indicating the format of the acknowledgement (ACK) frame of thecurrent packet.

In some embodiments, the coding field of the short preamble in Table 1includes a first bit to indicate whether BCC or LDPC encoding is used,and a second bit to indicate an extra symbol during LDPC encoding. Inone such embodiment, however, the duplicate mode is only used with BCCencoding. To indicate duplicate mode, in this embodiment, the first bitof the coding field indicates that BCC encoding is used, while thesecond bit (which would otherwise be a “reserved” bit for BCC encoding)is used to indicate the duplicate mode to a receiver. Thus, in thisembodiment, the second bit of the coding field indicates either 1)whether there is an extra symbol (if the first bit indicates LDPCencoding) or 2) whether the long range data unit is a duplicate modedata unit (if the first bit indicates BCC encoding). In otherembodiments (e.g., embodiments where the duplicate mode is notrestricted to BCC encoding), one of the “reserved” bits in the shortand/or long preamble of Table 1 is instead designated as a “duplicatefield,” and used to indicate whether the long range data unit is aduplicate mode data unit.

In some embodiments in which the duplicate mode is indicated in the SIG(or SIGA) field (e.g., in the MCS field, in the coding field, or in adedicated “duplicate field,” in various embodiments), a receiver maychoose to coherently combine the 2 MHz signals in each of two or moredifferent 2 MHz sub-bands to improve reception. In one embodiment andscenario, for example, a receiver learns from the SIG or SIGA field thata current long range data unit is a duplicate mode data unit, and inresponse performs MRC combining on the different 2 MHz sub-band signalsbefore decoding the duplicated 2 MHz signal. By utilizing MRC combiningon the 2 MHz sub-bands, both combining gain and diversity gain may beachieved, thereby allowing the long range data unit to be correctlyreceived and decoded at a lower signal-to-noise ratio (SNR) point.

In some embodiments, the long range communication protocol only allowsthe duplicate mode for data units with a data portion, such as dataportion 504 of long range data unit 500 in FIG. 7A or data portion 524of long range data unit 520 in FIG. 7B. In various other embodiments,however, the long range communication protocol instead, or additionally,allows a duplicate mode for null data packet (NDP) short MAC frames thatdo not include a data portion. In one embodiment, the duplicate mode isthe same for NDP short MAC frames as the duplicate mode described abovewith reference to long range data units (e.g., STF, LTF and SIG fieldare duplicated in each 2 MHz sub-band), except that the data portion isomitted. Various types of NDP control frames (e.g., NDP short ACK framesor NDP short CTS frames) are described in U.S. patent application Ser.No. 13/586,678.

FIG. 8 is a diagram of an example duplicate mode 4 MHz long range NDP560, according to one such embodiment. The duplicate mode 4 MHz longrange NDP 560 includes a duplicated STF 562, a duplicated LTF1 564, anda duplicated SIG field 566, similar to the duplicated STF 510,duplicated LTF1 512, and duplicated SIG field 514 in the long range dataunit 500 of FIG. 7A, in an embodiment. Unlike the long range data unit500, however, the duplicate mode 4 MHz long range NDP 560 does notinclude a data portion. In one embodiment, the duplicate mode 4 MHz longrange NDP 560 is a short ACK frame used to protect the full 4 MHzbandwidth of a 4 MHz BSS channel.

In an alternative embodiment, an NDP short MAC frame in a 4 MHzbandwidth directly uses the true 4 MHz NDP short MAC frame for bandwidthprotection. In this embodiment, the LTF1 of the 4 MHz NDP short MACframe uses the tone plan of a true 4 MHz signal (e.g., having sixlower-edge and five upper-edge guard tones), and the SIG field in each 2MHz sub-band has the same number of lower-edge and upper-edge guardtones as the LTF1 (e.g., the same as a 10× down-clocked IEEE 802.11a/glegacy packet with the lowest data rate, in an embodiment). Becausethere is no data portion, the LTF1 tone plan is sufficient for areceiver to decode the 2 MHz SIG field in each 2 MHz sub-band of the 4MHz NDP short MAC frame. In some embodiments, duplicate mode NDP framescan also be generated in wider bandwidths (e.g., 8 MHz and/or 16 MHz) byutilizing additional frequency duplicates.

In some embodiments, the long range communication protocol applies adifferent phase shift to the duplicated 2 MHz long range data unit ineach 2 MHz sub-band, in order to reduce the PAPR of the signal. In oneembodiment, for example, a phase shift of [1, j] is applied to the two 2MHz sub-bands of a duplicate mode 4 MHz long range data units (i.e., nophase shift to the lower 2 MHz sub-band, and a 90 degree phase shift tothe upper 2 MHz sub-band), and a phase shift of [1, −1, −1, −1] isapplied to the four 2 MHz sub-bands of a duplicate mode 8 MHz long rangedata unit (i.e., no phase shift to the lowest 2 MHz sub-band, and a 180degree phase shift to each of the upper three 2 MHz sub-bands). In oneembodiment where phase shifts are applied to the various 2 MHzsub-bands, the phase shifts are applied to both the preamble and thedata portion of the respective 2 MHz sub-band. In some embodiments wherethe long range communication protocol allows duplicate mode for NDPframes, a similar set of phase shifts is applied to the 2 MHz sub-bandsof each duplicate mode NDP frame.

FIG. 9 is a flow diagram of an example method 600 for generating OFDMsignals to be transmitted in a BSS channel, according to an embodiment.The method 600 is used in a communication network that employs achannelization scheme in which a set of two or more component channelscan be aggregated to form the BSS channel (e.g., the channelizationscheme 40 of FIG. 2, in an embodiment). In an embodiment, the componentchannel bandwidth is equal to the lowest permissible BSS channelbandwidth (e.g., 2 MHz in an embodiment where 2/4/8/16 MHz BSS channelbandwidths are permitted). In various embodiments and scenarios, themethod 600 is implemented by the network interface 16 of AP 14, or bythe network interface 27 of station 25-1, in FIG. 1, for example.

In an embodiment, the communication device implementing the method 600operates according to a long range communication protocol that definesboth a non-duplicate mode data unit corresponding to a single componentchannel within the component channels of the BSS channel, and anon-duplicate mode data unit corresponding to a set of adjacentcomponent channels within the component channels of the BSS channel. Theset of adjacent component channels is the same as (i.e., collectivelycoextensive with) the BSS channel (e.g., one of channels 44, 46 or 48 inFIG. 2), in some embodiments and/or scenarios. In other embodimentsand/or scenarios, the set of adjacent component channels occupies lessthan the entire BSS channel. In some embodiments where each componentchannel has a 2 MHz bandwidth, the set of adjacent component channelshas a total bandwidth of 2^(N)*(2 MHz), where N is an integer greaterthan zero.

In an embodiment, the communication protocol specifies that anon-duplicate mode data unit corresponding to the set of adjacentcomponent channels (e.g., a 4 MHz or greater non-duplicate mode dataunit) has more lower-edge guard tones, and/or more upper-edge guardtones, than a non-duplicate mode data unit corresponding to a singlecomponent channel (e.g., a 2 MHz non-duplicate mode data unit). In oneembodiment, for example, a non-duplicate mode data unit corresponding toa single component channel has the tone map 200 of FIG. 4A, and anon-duplicate mode data unit corresponding to the set of adjacentcomponent channels is either a true 4 MHz data unit having the tone map220 of FIG. 4B, or a true 8 MHz data unit having the tone map 300 ofFIG. 5A.

At block 602, it is determined that a duplicate mode will be utilizedfor an OFDM transmission. In one embodiment and scenario, for example,it is determined that a duplicate mode will be utilized as a result ofdetecting poor channel conditions (e.g., in order to achieve diversitygain and/or combining gain). In one embodiment and/or scenario, adecision as to whether the duplicate mode will be used was initiallymade at an earlier time, and the determination at block 602 is made bychecking the value of an indicator or flag that was set based on thatearlier decision.

At block 604, a duplicate mode data unit corresponding to the set ofadjacent component channels (e.g., the full BSS channel, in oneembodiment and/or scenario) is generated in response to determining atblock 602 that the duplicate mode will be utilized. The duplicate modedata unit is generated such that the duplicate mode data unit includes,for each component channel in the set of adjacent component channels,one duplicate (in frequency) of the non-duplicate mode data unitcorresponding to a single component channel. Thus, the duplicate modedata unit is generated such that the duplicate mode data unit has fewerlower-edge guard tones and/or fewer upper-edge guard tones than anon-duplicate mode data unit corresponding to the same set of adjacentcomponent channels. In one embodiment, the generated duplicate mode dataunit has the same number of lower-edge guard tones and the same numberof upper-edge guard tones as the non-duplicate mode data unitcorresponding to the single component channel. For example, in oneembodiment where the communication protocol defines the non-duplicatemode data unit corresponding to the single component channel as havingthe tone map 200 of FIG. 4A, and defines the non-duplicate mode dataunit corresponding to the set of adjacent component channels as havingthe tone map 220 of FIG. 4B, the duplicate mode data unit is generatedsuch that the duplicate mode data unit has the tone map 240 of FIG. 4C.

In one embodiment where the set of adjacent component channels has atotal bandwidth of 2^(N)*(2 MHz), with N being an integer greater thanzero, generating the duplicate mode data unit at block 604 includesutilizing an IFFT of size 32*(N+1). In one embodiment, generating theduplicate mode data unit at block 604 includes multiplying eachduplicate by a different phase rotation multiplier, in order to reducePAPR of the duplicate mode data unit signal.

In an embodiment, the non-duplicate mode data unit corresponding to thesingle component channel includes both a preamble and a data portion,and the duplicate mode data unit generated at block 604 therefore alsoincludes a (duplicated) preamble and data portion (e.g., as shown inFIG. 7A or 7B, in an embodiment). In an alternative embodiment, theduplicate mode data unit generated at block 604 duplicates the dataportion of the non-duplicate mode data unit corresponding to the singlecomponent channel, but not the preamble (or not the entire preamble). Inone embodiment, for example, the duplicate mode data unit generated atblock 604 duplicates a data portion, STF and SIG field, but not the LTF,of the non-duplicate mode data unit corresponding to the singlecomponent channel, with the LTF instead having the same tone map as theLTF of the non-duplicate mode data unit corresponding to the set ofadjacent component channels.

In some embodiments where the non-duplicate mode data unit correspondingto the single component channel includes a preamble with a SIG field,the SIG field includes a bandwidth field indicating a bandwidth to areceiving device. In one such embodiment, generating the duplicate modedata unit at block 604 includes setting the bandwidth field in eachduplicate of the SIG field to indicate a bandwidth equal to thebandwidth of the single component channel (e.g., 2 MHz). In analternative embodiment, the bandwidth field in each duplicate is set toindicate a total bandwidth of the set of adjacent component channels(e.g., 4 MHz or greater), i.e., the full bandwidth of duplicate modedata unit generated at block 604. In this latter alternative embodiment,a receiver may be unable to detect the duplicate mode based on thebandwidth field (and therefore unable to perform MRC combining of theSIG field, for example). Thus, in one such embodiment, a different fieldwithin the SIG field indicates the duplicate mode to a receiver. Invarious embodiments, for example, an MCS field, coding field, dedicated“duplicate field,” or other suitable field within the SIG fieldindicates that the data unit generated at block 604 is a duplicate modedata unit.

In one embodiment, the method 600 includes an additional block (notshown in FIG. 9), prior to block 604 (and/or prior to block 602) inwhich it is determined that the set of adjacent component channels willbe utilized for the OFDM transmission. In one embodiment where themethod 600 is implemented within the station 25-1, for example, thenetwork interface 27 of station 25-1 determines that the set of adjacentcomponent channels will be utilized based on information specifying theset of adjacent component channels channel received from the AP 14(e.g., by receiving an indicator of the BSS channel, in an embodimentwhere the adjacent component channels are coextensive with the BSSchannel). In another embodiment, where the method 600 is implementedwithin the AP 14, the network interface 16 of AP 14 directly determinesthe set of adjacent component channels using a known media accesstechnique. In other embodiments and/or scenarios, the set of adjacentcomponent channels to be utilized is determined by checking the value ofa previously set flag or other indicator.

Further, in one embodiment, the method 600 includes an additional block(not shown in FIG. 9) in which the duplicate mode data unit generated atblock 604 is transmitted, or caused to be transmitted, to one or morecommunication devices other than the communication device implementingthe method 600. In this embodiment, the duplicate mode data unit istransmitted, or caused to be transmitted, such that each duplicate ofthe non-duplicate mode data unit corresponding to the single componentchannel is transmitted via a different component channel of the set ofadjacent component channels.

In some scenarios, the method 600 (or only step 604 of the method 600)is repeated for multiple iterations to generate multiple duplicate modedata units. Moreover, in some embodiments and scenarios, a methodsimilar to method 600 is performed to generate one or more additionalduplicate mode data units having different bandwidths. For example, inone embodiment where the method 600 generates a 4 MHz duplicate modedata unit containing two 2 MHz data unit duplicates, additional stepssimilar to blocks 602 and 604 may be performed a second time to generatean 8 MHz duplicate mode data unit containing four 2 MHz data unitduplicates, a third time to generate a 16 MHz duplicate mode data unitcontaining eight 2 MHz data unit duplicates, etc.

In some embodiments, the long range communication protocol defines notonly non-duplicate mode and duplicate mode data units that correspond toa BSS channel (e.g., 2 MHz, 4 MHz, 8 MHz, or 16 MHz, in an embodiment),but also “low bandwidth mode” data units that are transmitted over abandwidth smaller than any BSS channel (e.g., over a 1 MHz bandwidth)and have a lower data rate. In one embodiment where a “normal mode”(i.e., not corresponding to the low bandwidth mode) 2 MHz or greaterdata unit is generated using a 64-point or greater IFFT, for example, alow bandwidth mode 1 MHz data unit is generated using a 32-point IFFT.The lower data rate of the low bandwidth mode data unit allows the lowbandwidth mode to further extend communication range, which generallyimproves receiver sensitivity, in an embodiment. In various embodiments,the low bandwidth mode is used only as a control mode (e.g., for signalbeacon or association procedures, transmit beamforming trainingoperations, etc.), only for extended range data communications, or both.Example formats of low bandwidth mode data units, and the generation ofsuch data units, according to various embodiments, are described in U.S.patent application Ser. No. 13/366,064, “Control Mode PHY for WLAN,” andU.S. patent application Ser. No. 13/494,505, “Low Bandwidth PHY forWLAN,” the disclosures of which are hereby incorporated by referenceherein.

In various embodiments and/or scenarios, low bandwidth mode data unitsare transmitted within channels defined by the long range communicationprotocol, either singly (e.g., a 1 MHz transmission in a 2 MHz orgreater channel bandwidth) or in duplicate (e.g., two or more duplicatesor replicas, in the frequency domain, of a 1 MHz transmission in a 2 MHzor greater channel bandwidth). Example embodiments utilizing duplicationof low bandwidth mode data units in wider BSS channel bandwidths aredescribed in U.S. patent application Ser. No. 13/586,678, “Long RangeWLAN Data Unit Format,” and U.S. patent application Ser. No. 13/768,876,“Low Bandwidth PHY Transmission in a Wider Bandwidth,” the disclosuresof which are hereby incorporated by reference herein. Moreover, in someembodiments, the long range communication protocol defines a special MCSfor low bandwidth mode data units in which low-order modulation (e.g.,BPSK) and low-rate coding (e.g., rate 1/2 coding) are used along withtime-domain repetition, e.g., in order to further extend communicationrange. Example embodiments utilizing time-domain repetition for lowbandwidth mode data units are described in U.S. patent application Ser.No. 13/494,505, “Low Bandwidth PHY for WLAN.”

In some embodiments where the long range communication protocol definesboth normal mode and low bandwidth mode data units, the long rangecommunication protocol only allows duplication of normal mode dataunits, such as the example long range data unit 500 of FIG. 7A or theexample long range data unit 520 of FIG. 7B. In other embodiments, thelong range communication protocol additionally allows duplication of lowbandwidth mode data units. In one embodiment where duplication of 1 MHzlow bandwidth mode data units is allowed, a 2 MHz or wider duplicatemode signal (e.g., 2 MHz, 4 MHz, 8 MHz or 16 MHz, in one embodiment)formed by duplicating the 1 MHz low bandwidth mode data unit results inonly three lower-edge guard tones and two upper-edge guard tones, andrelatively strict filter design requirements.

In some embodiments, the long range communication protocol only allows a1 MHz low bandwidth mode data unit to be transmitted in one 1 MHzsub-band of a BSS channel. In one embodiment, for example, a 1 MHz lowbandwidth mode data unit can only be transmitted in a lower 1 MHzsub-band of a 2 MHz BSS channel. In another example embodiment, a 1 MHzlow bandwidth mode data unit can only be transmitted in a lower 1 MHzsub-band of a 2 MHz primary channel within a 4 MHz or greater bandwidthBSS channel, so long as the 2 MHz primary channel is not located at thelowest 2 MHz sub-band of the BSS channel. In this embodiment, however,the 1 MHz low bandwidth mode data unit is transmitted in the upper halfof the 2 MHz primary channel if the 2 MHz primary channel is located atthe lowest 2 MHz sub-band of the BSS channel, in order to avoid the 1MHz low bandwidth mode data unit being located at an edge of the BSSchannel.

In other embodiments, frequency duplication of 1 MHz low bandwidth modedata units is used to provide bandwidth protection against a 1 MHz OBSS.In one embodiment, for example, the 1 MHz low bandwidth mode data unitis duplicated in each 1 MHz sub-band of a wider bandwidth signal (e.g.,2 MHz, 4 MHz, 8 MHz or 16 MHz), with the spectral mask of a true, widerbandwidth signal being met by scaling down or zeroing out one or moretones. In one embodiment where each 1 MHz low bandwidth mode data unithas three lower-edge and two upper-edge guard tones, for example, a 2MHz data unit formed by duplicating a 1 MHz low bandwidth mode data unitcan meet the true 2 MHz signal spectral mask by zeroing out or scalingdown the upper-most tone of the 1 MHz low bandwidth mode data unit thatis in the upper 1 MHz sub-band. In an embodiment, phase rotations areapplied to each 1 MHz sub-band when a 1 MHz low bandwidth mode data unitis duplicated (e.g., phase rotations of [1, j] for a 2 MHz signal formedby duplicating the 1 MHz low bandwidth mode data unit). In theseembodiments, because the STF and LTF are duplicated in each 1 MHzsub-band, each 1 MHz sub-band looks to a receiver like a stand-alone 1MHz low bandwidth mode data unit. Therefore, a device setting its devicefilter bandwidth to only 1 MHz can still receive such a data unit, ascan a device setting its device filter bandwidth to 2 MHz or greater.For both such devices, no extra processing (beyond that already neededfor regular 1 MHz data unit reception) is required because both devicescan receive the data unit as a stand-alone 1 MHz data unit in a single 1MHz sub-band.

Other embodiments for locating a 1 MHz low bandwidth mode data unit, orduplicates thereof, within a BSS channel (including embodiments in whichone or more tones are zeroed out or scaled down), are described in U.S.patent application Ser. No. 13/768,876.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, one or moreprocessors executing firmware instructions, one or more processorsexecuting software instructions, or any combination thereof. Whenimplemented utilizing one or more processors executing software orfirmware instructions, the software or firmware instructions may bestored in any computer readable memory such as on a magnetic disk, anoptical disk, or other storage medium, in a RAM or ROM or flash memory,processor, hard disk drive, optical disk drive, tape drive, etc.Likewise, the software or firmware instructions may be delivered to auser or a system via any known or desired delivery method including, forexample, on a computer readable disk or other transportable computerstorage mechanism or via communication media. Communication mediatypically embodies computer readable instructions, data structures,program modules or other data in a modulated data signal such as acarrier wave or other transport mechanism. The term “modulated datasignal” means a signal that has one or more of its characteristics setor changed in such a manner as to encode information in the signal. Byway of example, and not limitation, communication media includes wiredmedia such as a wired network or direct-wired connection, and wirelessmedia such as acoustic, radio frequency, infrared and other wirelessmedia. Thus, the software or firmware instructions may be delivered to auser or a system via a communication channel such as a telephone line, aDSL line, a cable television line, a fiber optics line, a wirelesscommunication channel, the Internet, etc. (which are viewed as being thesame as or interchangeable with providing such software via atransportable storage medium). The software or firmware instructions mayinclude machine readable instructions that, when executed by the one ormore processors, cause the one or more processors to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe claims.

What is claimed is:
 1. A method, in a communication device operatingaccording to a communication protocol, for generating orthogonalfrequency division multiplexing (OFDM) signals to be transmitted in abasic service set (BSS) channel, wherein a set of two or more componentchannels is collectively coextensive with the BSS channel, wherein thecommunication protocol defines (i) a non-duplicate mode data unitcorresponding to a single component channel within the set of two ormore component channels and (ii) a non-duplicate mode data unitcorresponding to a first set of adjacent component channels within theset of two or more component channels, wherein the non-duplicate modedata unit corresponding to the single component channel has (i) a firstnumber of lower-edge guard tones and (ii) a first number of upper-edgeguard tones, wherein the non-duplicate mode data unit corresponding tothe first set of adjacent component channels has (i) a second number oflower-edge guard tones and (ii) a second number of upper-edge guardtones, and wherein at least one of (i) the second number of lower-edgeguard tones is greater than the first number of lower-edge guard tonesor (ii) the second number of upper-edge guard tones is greater than thefirst number of upper-edge guard tones, the method comprising:determining, at the communication device, that a duplicate mode will beutilized for a first OFDM transmission in the first set of adjacentcomponent channels; and in response to determining that the duplicatemode will be utilized for the first OFDM transmission, generating, atthe communication device, a first duplicate mode data unit correspondingto the first set of adjacent component channels, such that the firstduplicate mode data unit has one or both of (i) less than the secondnumber of lower-edge guard tones and (ii) less than the second number ofupper-edge guard tones, wherein the first duplicate mode data unitincludes, for each component channel in the first set of adjacentcomponent channels, one duplicate, in frequency, of the non-duplicatemode data unit corresponding to the single component channel.
 2. Themethod of claim 1, wherein generating the first duplicate mode data unitincludes generating the first duplicate mode data unit such that thefirst duplicate mode data unit has (i) the first number of lower-edgeguard tones and (ii) the first number of upper-edge guard tones.
 3. Themethod of claim 1, further comprising: transmitting the first duplicatemode data unit to one or more other communication devices such that eachduplicate of the non-duplicate mode data unit corresponding to thesingle component channel is transmitted via a different componentchannel of the first set of adjacent component channels.
 4. The methodof claim 1, wherein the non-duplicate mode data unit corresponding tothe single component channel includes a preamble and a data portion. 5.The method of claim 4, wherein: the preamble includes a signal field;the signal field includes a bandwidth field; and generating the firstduplicate mode data unit includes setting the bandwidth field in eachduplicate to indicate a bandwidth equal to a bandwidth of the singlecomponent channel.
 6. The method of claim 4, wherein: the preambleincludes a signal field; the signal field includes a bandwidth field;and generating the first duplicate mode data unit includes setting thebandwidth field in each duplicate to indicate a bandwidth equal to atotal bandwidth of the first set of adjacent component channels.
 7. Themethod of claim 6, wherein: the signal field further includes amodulation and coding scheme (MCS) field; and generating the firstduplicate mode data unit includes setting the MCS field in eachduplicate to indicate that the first duplicate mode data unitcorresponds to the duplicate mode.
 8. The method of claim 6, wherein:the signal field further includes a coding field; and generating thefirst duplicate mode data unit includes setting the coding field in eachduplicate to indicate that the first duplicate mode data unitcorresponds to the duplicate mode.
 9. The method of claim 6, wherein:the signal field further includes a duplicate field; and generating thefirst duplicate mode data unit includes setting the duplicate field ineach duplicate to indicate that the first duplicate mode data unitcorresponds to the duplicate mode.
 10. The method of claim 1, whereinthe communication protocol further defines a non-duplicate mode dataunit corresponding to a second set of adjacent component channels withinthe set of two or more component channels, wherein the second set ofadjacent component channels includes more component channels than thefirst set of adjacent component channels, wherein the non-duplicate modedata unit corresponding to the second set of adjacent component channelshas (i) a third number of lower-edge guard tones and (ii) a third numberof upper-edge guard tones, and wherein at least one of (i) the thirdnumber of lower-edge guard tones is greater than the first number oflower-edge guard tones or (ii) the third number of upper-edge guardtones is greater than the first number of upper-edge guard tones, themethod further comprising: determining, at the communication device,that the duplicate mode will be utilized for a second OFDM transmissionin the second set of adjacent component channels; and in response todetermining that the duplicate mode will be utilized for the second OFDMtransmission, generating, at the communication device, a secondduplicate mode data unit corresponding to the second set of adjacentcomponent channels, such that the second duplicate mode data unit hasone or both of (i) less than the third number of lower-edge guard tonesand (ii) less than the third number of upper-edge guard tones, whereinthe second duplicate mode data unit includes, for each component channelin the second set of adjacent component channels, one duplicate, infrequency, of the non-duplicate mode data unit corresponding to thesingle component channel.
 11. The method of claim 1, wherein generatingthe first duplicate mode data unit includes multiplying each duplicateof the non-duplicate mode data unit corresponding to the singlecomponent channel by a different phase rotation multiplier.
 12. Themethod of claim 1, wherein: each component channel in the set of two ormore component channels has a 2 MHz bandwidth; the first set of adjacentcomponent channels has a total bandwidth of 2^(N)*(2 MHz), where N is aninteger greater than zero; and generating the first duplicate mode dataunit includes utilizing an inverse fast Fourier transform (IFFT) of size32*(N+1).
 13. The method of claim 1, further comprising: beforegenerating the first duplicate mode data unit, determining, at thecommunication device, that the first set of adjacent component channelswill be utilized for the first OFDM transmission.
 14. A communicationdevice comprising: a network interface configured to operate accordingto a communication protocol, wherein the communication protocol defines(i) a non-duplicate mode data unit corresponding to a single componentchannel within a set of two or more component channels collectivelycoextensive with a basic service set (BSS) channel, and (ii) anon-duplicate mode data unit corresponding to a set of adjacentcomponent channels within the set of two or more component channels, thenon-duplicate mode data unit corresponding to the single componentchannel has (i) a first number of lower-edge guard tones and (ii) afirst number of upper-edge guard tones, the non-duplicate mode data unitcorresponding to the set of adjacent component channels has (i) a secondnumber of lower-edge guard tones and (ii) a second number of upper-edgeguard tones, and at least one of (i) the second number of lower-edgeguard tones is greater than the first number of lower-edge guard tonesor (ii) the second number of upper-edge guard tones is greater than thefirst number of upper-edge guard tones, determine that a duplicate modewill be utilized for an orthogonal frequency division multiplexing(OFDM) transmission in the set of adjacent component channels, and inresponse to determining that the duplicate mode will be utilized for theOFDM transmission, generate a duplicate mode data unit corresponding tothe set of adjacent component channels, such that the duplicate modedata unit has one or both of (i) less than the second number oflower-edge guard tones and (ii) less than the second number ofupper-edge guard tones, wherein the duplicate mode data unit includes,for each component channel in the set of adjacent component channels,one duplicate, in frequency, of the non-duplicate mode data unitcorresponding to the single component channel.
 15. The communicationdevice of claim 14, wherein the network interface is further configuredto: transmit the duplicate mode data unit to one or more othercommunication devices such that each duplicate of the non-duplicate modedata unit corresponding to the single component channel is transmittedvia a different component channel of the set of adjacent componentchannels.
 16. The communication device of claim 14, wherein: thenon-duplicate mode data unit corresponding to the single componentchannel includes a preamble and a data portion; the preamble includes asignal field; the signal field includes a bandwidth field; and thenetwork interface is configured to generate the duplicate mode data unitat least in part by setting the bandwidth field in each duplicate toindicate a bandwidth equal to a bandwidth of the single componentchannel.
 17. The communication device of claim 14, wherein the networkinterface is configured to generate the duplicate mode data unit atleast in part by multiplying each duplicate of the non-duplicate modedata unit corresponding to the single component channel by a differentphase rotation multiplier.
 18. A nontransitory computer-readable mediumstoring instructions for operating according to a communicationprotocol, wherein the communication protocol defines (i) a non-duplicatemode data unit corresponding to a single component channel within a setof two or more component channels collectively coextensive with a basicservice set (BSS) channel and (ii) a non-duplicate mode data unitcorresponding to a set of adjacent component channels within the set oftwo or more component channels, wherein the non-duplicate mode data unitcorresponding to the single component channel has (i) a first number oflower-edge guard tones and (ii) a first number of upper-edge guardtones, wherein the non-duplicate mode data unit corresponding to the setof adjacent component channels has (i) a second number of lower-edgeguard tones and (ii) a second number of upper-edge guard tones, andwherein at least one of (i) the second number of lower-edge guard tonesis greater than the first number of lower-edge guard tones or (ii) thesecond number of upper-edge guard tones is greater than the first numberof upper-edge guard tones, and wherein the instructions, when executedby one or more processors, cause the one or more processors to:determine that a duplicate mode will be utilized for an orthogonalfrequency division multiplexing (OFDM) transmission in the set ofadjacent component channels; in response to determining that theduplicate mode will be utilized for the OFDM transmission, generate aduplicate mode data unit corresponding to the set of adjacent componentchannels, such that the duplicate mode data unit has one or both of (i)less than the second number of lower-edge guard tones and (ii) less thanthe second number of upper-edge guard tones, wherein the duplicate modedata unit includes, for each component channel in the set of adjacentcomponent channels, one duplicate, in frequency, of the non-duplicatemode data unit corresponding to the single component channel.
 19. Thenontransitory computer-readable medium of claim 18, wherein: thenon-duplicate mode data unit corresponding to the single componentchannel includes a preamble and a data portion; the preamble includes asignal field; the signal field includes a bandwidth field; and theinstructions cause the one or more processors to generate the duplicatemode data unit at least in part by setting the bandwidth field in eachduplicate to indicate a bandwidth equal to a bandwidth of the singlecomponent channel.
 20. The nontransitory computer-readable medium ofclaim 18, wherein the instructions cause the one or more processors togenerate the duplicate mode data unit at least in part by multiplyingeach duplicate of the non-duplicate mode data unit corresponding to thesingle component channel by a different phase rotation multiplier.